The present invention pertains to a technical field of a seat belt device for restraining an occupant which is provided for a seat of a vehicle such as an automobile. More particularly, the present invention pertains to a technical field of a buckle on which extreme inertia force is exerted by, for example, pulling action by a pre-tensioner when a seat belt device restraints an occupant.
Nowadays, in various vehicles including automobiles, seat belt devices for protecting occupants in emergency such as collision are mounted for seats thereof. In order to facilitate the occupant to wear on and off such a seat belt, a buckle is normally provided. In general, the buckle comprises a latch member provided with a joggle portion which latches a tongue. The engagement and disengagement between the tongue and the buckle are achieved by that the latch member is biased by a spring in such a direction as to latch the tongue and by that the latch member is pivoted by an operational button in such a direction as to release the tongue.
A buckle of a type that is pulled by a pre-tensioner when the seat belt restraints an occupant is known in the art. The buckle of this type is rapidly pulled by the pre-tensioner so as to cause extreme acceleration. Because of this acceleration, inertia force is developed in a direction opposite to the direction of the acceleration. Due to the inertia force, there is a possibility of unexpected disengagement between the tongue and the buckle.
Therefore, a buckle for a safety belt has been proposed in Japanese Patent Unexamined Publication No. 08-228809, which can securely prevent such unexpected disengagement between a tongue and the buckle even when the buckle is subjected to extreme acceleration.
In the buckle disclosed in this publication, a release button has a pair of limit stops spaced from each other with a predetermined distance and, on the other hand, a lever has a pair of first and second lever arms, which are formed integrally with each other, and a mass body. The first and second lever arms and the mass body are disposed on a frame in such a manner that they can rotate together. The first lever arm is located to confront one of the limit stops of the release button and the second lever arm is located to confront the other one of the limit stops.
In case of normal releasing operation of the release button, one limit stop strikes the first lever arm and pivots the first and second lever arms and the mass body while the release button moves in a direction of disengaging the tongue from buckle. As extreme acceleration is exerted on the buckle in a direction opposite to the disengaging direction of the release button, inertia force in the disengaging direction of the release button is developed on the release button, the first and second lever arms, and the mass body, so the first and second lever arms and the mass body are pivoted whereby the first lever arm is brought in contact with one of the limit stops. Since the release button is therefore prevented from moving in the disengaging direction, the disengagement between the tongue and the buckle is prevented. As extreme acceleration is exerted on the buckle in the disengaging direction of the release button, inertia force in the direction opposite to the disengaging direction of the release button is developed on the release button, the first and second lever arms, and the mass body, so the first and second lever arms are pivoted whereby the second lever arm is brought in contact with the other limit stop. This prevents the release button from moving in the direction opposite to the disengaging direction.
In the buckle disclosed in the publication, unexpected disengagement between the tongue and the buckle during extreme acceleration or deceleration can be securely prevented.
In case that the buckle is pulled by the pre-tensioner, the terminal of this pulling action causes acceleration in a direction opposite to that of the acceleration developed during the pulling action. This acceleration exerts inertia force on the buckle in the direction opposite to that of the acceleration. That is, there is a possibility that the direction of inertia force is suddenly reversed at the termination of the pulling action by the pre-tensioner. Such sudden reversion may cause unexpected disengagement between the tongue and the buckle.
In the buckle disclosed in the aforementioned publication, however, since the first and second lever arms and the mass body are formed integrally with each other, the inertia moment must be large. Therefore, it is quite difficult to reverse the direction of the lever which is pivoted. Accordingly, it should be difficult to securely correspond such sudden reversion of the direction of the inertia force to prevent the unexpected disengagement between the tongue and the buckle.
Since the first and second lever arm and the mass body are pivoted together during the movement of the release button in the disengaging direction, larger operating force is required as compared to a case where only the release button is moved, so it is hard to say that the operational feeling of the buckle is excellent without any problem.
Further, the limit stops of the release button make the release button's configuration special so that the release button does not have interchangeability with release buttons of other buckles. The first and second lever arms are disposed on a frame separate from the release button while the limit stops are disposed on the release button. In order to secure the operation of the limit stops and the first and second lever arms, the spaces among them should be exactly set, so it is hard to say that the assembly condition of the release button, the first and second lever arms is excellent.